I actually am aware of Slate's purchase, lots of chatter on SSP about it considering it's such a massive investment and seems to be a rare instance of reusing legacy industrial land for modern industrial uses. The potential with the site is a bit different from typical employment areas, I think; you effectively have a parcel with lake, rail, and highway access all bundled into one (emphasis on the lake- not many places around that offer deep-water shipping access). And, it is an absolutely huge site. It's shooting from ~800 jobs to over 25,000. It is going to be a great city-building project and will hopefully revitalize the north end dramatically. A fantastic scheme if you ask me.
I wasn't aware that Oakville had lands along the 407, though, or any of the other plans you mentioned. Do you find these just by combing through municipal land use plans? It is unfortunate that employment areas seem to be mostly planned on a municipal level and seem to have little coordination with the province. Would certainly make it easier to understand them. They don't show up in regional plans often, despite occupying huge swathes of space. The Neptis foundation was good for addressing their lack of attention on a planning level.